Central venous pressure (CVP) increases with worsening heart failure. As CVP increases, vein diameter increases. During clinical examination of heart failure patients, echocardiography can be used to monitor vein diameter as an indicator of CVP. Diagnosis of high CVP is useful in managing the treatment of heart failure patients. Implantable medical devices are available or have been proposed for providing ambulatory monitoring of physiological signals associated with heart failure, such as intracardiac blood pressure, heart rhythm, blood oxygen levels, heart wall motion, and lung edema. It is desirable to provide ambulatory monitoring of CVP in heart failure patients for use in managing heart failure treatment.